Taken from https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-devel/llvm-roc/files

diff -Naur a/clang/lib/Basic/CMakeLists.txt b/clang/lib/Basic/CMakeLists.txt
--- a/clang/lib/Basic/CMakeLists.txt	2019-12-28 07:42:49.119055933 +0100
+++ b/clang/lib/Basic/CMakeLists.txt	2019-12-28 07:42:13.265056070 +0100
@@ -2,6 +2,7 @@
   Core
   MC
   Support
+  Option
   )
 
 find_first_existing_vc_file("${LLVM_MAIN_SRC_DIR}" llvm_vc)
diff -Naur a/clang/lib/Driver/CMakeLists.txt b/clang/lib/Driver/CMakeLists.txt
--- a/clang/lib/Driver/CMakeLists.txt	2019-12-28 07:41:39.521056199 +0100
+++ b/clang/lib/Driver/CMakeLists.txt	2019-12-28 07:40:23.998056487 +0100
@@ -79,4 +79,5 @@
   LINK_LIBS
   clangBasic
   ${system_libs}
+  pthread
   )
